1. Field of the Invention
This invention relates to a method and apparatus for measuring seat occupant weight and eliminating error caused by over tightened seat belts to improve airbag deployment control. Specifically, a compensation factor is determined based on seat occupant weight to correct error caused by an over-tight seat belt used to secure a child seat to a vehicle seat.
2. Related Art
Most vehicles include airbags and seatbelt restraint systems that work together to protect the driver and passengers from experiencing serious injuries due to a high speed collision. It is important to control the deployment force of the airbags based on the size of the driver or the passenger. When an adult is seated on the vehicle seat, the airbag should be deployed in a normal manner. If there is an infant seat secured to the vehicle seat then the airbag should not be deployed or should be deployed at a significantly lower deployment force. One way to control the airbag deployment is to monitor the weight of the seat occupant.
There are several different sensing systems that measure the weight of a seat occupant. One type of system uses pressure sensitive foil mats mounted within the seat bottom foam. Another system uses sensors placed at a plurality of locations within the seat bottom. The combined output from the mats or the sensors is used to determine the weight of the seat occupant.
These current sensor systems can have difficulty determining whether an adult is belted to the seat or whether a child car seat is belted to the seat. When a child seat is secured to the seat with a seat belt, an excess force acts on the sensors mounted within the rear portion of the seat, which interferes with accurate sensing of the weight of an occupant. Overtightening of the seatbelt, which makes it pull down on the rear of the seat, causes this force. The increased force causes the system to incorrectly detect a large child or small adult in the seat as opposed to a small child, resulting in airbag deployment instead of airbag suppression. Thus, due to this effect, the current weight sensing systems have difficulty in discerning between an adult occupant and a child in a child seat.
Thus, it is desirable to have a system for determining whether conditions are proper for deploying an airbag by determining whether a child in a child seat or an adult is belted to the seat. The system should further provide accurate measurements, be easy to install, and should overcome the above referenced deficiencies with prior art systems.
The subject invention provides a method and apparatus to compensate for loads induced by seat belt tension acting on a child seat or other similar occupant securely belted to a vehicle seat. Using the total measured occupant weight and the distribution of that weight on the vehicle seat, a compensation factor is generated for the belt-induced load. The compensation factor provides a reliable method of differentiating between a child seat with a large belt force and a small adult, thus resulting in proper airbag deployment control.
The method for correcting seat occupant weight measurement error induced by a seat belt includes the following steps. The seat occupant weight is measured and an asymmetry load is determined. The asymmetry load is the load that is applied to a vehicle seat based on a tension force generated by securing the occupant to the seat with a seat belt. A compensation factor is generated if the asymmetry load is greater than a minimum threshold and then the seat occupant weight is modified by the compensation factor. Preferably, the compensation factor is only generated if the weight is less than a predetermined weight. An airbag control signal is used to modify airbag deployment based on the corrected occupant weight
In a disclosed embodiment of this invention, the method differentiates between a child seat belted to the vehicle seat and a small adult. A seat occupant weight signal is generated representing the total measured weight of the child and child seat. An asymmetry load is determined based on the sensor and seat belt mounting locations. If the asymmetry load is above a predetermined minimum and if the occupant weight signal is less than a predetermined weight then the compensation factor is generated and the occupant weight signal is modified. The child seat is detected if the modified weight signal is less than a predetermined threshold and airbag deployment is suppressed if the child seat is detected.
The system for correcting seat occupant weight measurement error induced by a seat belt includes a vehicle seat having a seat back supported with respect to a seat bottom and a sensor assembly for measuring the weight of a seat occupant to generate a total measured seat occupant weight signal. A seat belt assembly secures the seat occupant to the vehicle seat and includes at least one seat belt mounting portion positioned adjacent to the vehicle seat for mounting the seat belt assembly to a vehicle structure. A control unit generates an asymmetry load based on the position of the seat belt mounting portion and the measured weight of the seat occupant and provides a compensation factor when the asymmetry loads exceeds a predetermined threshold. The compensation factor modifies the total measured seat occupant weight signal to correct weight measurement error induced by seat belt tension forces applied to the occupant. Preferably, the control unit detects a child seat when the modified signal is less than a predetermined limit and sends a control signal to an airbag controller to suppress airbag deployment.
Thus, the subject invention provides a simple, reliable, and accurate method and apparatus for differentiating between various types of seat occupants. These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.